Methods: After informed consent, patients with previously untreated renal and ureteric stones were admitted for an initial treatment by SWL between June 2008 and May 2009. Patients were randomly divided into two groups; one group received 3000 impulses at a rate of 60 impulses per minute, and the other received 4000 impulses at a rate of 90 impulses per minute. Patients submitted to re-treatment of the same stone were excluded. All treatments were done using the Dornier Compact Delta lithotripter. Stones were located by x-ray or ultrasound. Prior to treatment, patients were submitted to laboratory tests and a cardiologic evaluation when indicated. Urinary infections were treated prior to the SWL session. All procedures were performed under general anesthesia. Briefly, Tramadol 1-2 mg/kg associated to Propofol 2.5-3.0 mg/kg and scopolamine were employed in the majority of the procedures. Patients received 50-100 mg of diluted Tramadol and 20 mg of scopolamine just before the beginning of the SWL session and Propofol was maintained on continuous bomb infusion during the treatment and interrupted three minutes before the end of the session. All patients were maintained under spontaneous breathing, and a facial or a laryngeal oxygen mask was used according to the anesthesiologist's judgment. The potency of the lithotripter was increased progressively by 300 shocks until reaching the final stage, which occurred at a mean of 1500 shocks. The maximum potency employed was level 4 (equivalent to 14 kV) for renal stones and level 6 (16 kV) for ureteric stones.